1. Field of the Invention
The present invention relates to digital content protection, and more particularly, to protection of digital content in a digital rights management (DRM) system.
2. Description of the Related Art
As the world is moving from the analogue age to the digital age, more content is being created in digitized forms. While copying of analogue content requires much time and effort, digital content can be copied easily and quickly.
Also, while the quality of the analogue content is degraded in proportion to the frequency of copying, quality of the digital content is identically maintained regardless of the frequency of copying. Accordingly, protection of digital content has been desired and a variety of research projects for protection of digital content have been conducted by many companies.
FIG. 1 illustrates a conventional digital content protection environment.
Referring to FIG. 1, in the conventional digital content protection environment, a transmission stream is received through a variety of transmission channels and digital content is designed to be protected by using information included in the transmission stream.
In particular, a U.S. organization, Cable Television Laboratories, Inc. (CableLabs), ordered that copy control information (CCI) be attached to digital content in order to control copying of the content. The CCI is 2-bit information which restricts the number of times of digital content may be copied. The types of CCI includes copy free (00), copy once (01), copy no more (10) and copy never (11). Copy free indicates that copying the content is permitted without restriction. Copy once indicates that only one copy is permitted. If content with the CCI of copy once (01) is copied, the CCI of this content then becomes copy no more (10). Copy never indicates a prohibition on copying the content.
In order to prohibit unrestricted redistribution of high definition (HD)-level digital content broadcast in the U.S., the U.S. Federal Communications Commission (FCC) has ordered that a broadcast flag should be attached to digital content. The broadcast flag is 1-bit information indicating whether or not unrestricted redistribution of digital content is prohibited. The types of broadcast flag includes broadcast flag on (1) and broadcast flag off (0). Broadcast flag on indicates that unrestricted redistribution of digital content is not permitted, while broadcast flag off indicates that unrestricted redistribution of the digital content is permitted.
However, since the conventional methods of protecting digital content, such as the CCI and the broadcast flag, are very simple and limited in their options, it is difficult to protect digital content while also satisfying the needs of content consumers for freer usage of content. In addition, with only the conventional methods of the CCI and the broadcast flag, it is difficult to limit use to authorized users when the content is being distributed. Also, these methods are not effective to prevent content from being illegally redistributed to or used by many and unspecified persons.